Remember CDs? People used to store them in large metal towers and get them in packs of 12 from Columbia House. Now that you can listen to your Hootie & the Blowfish albums on Spotify and iTunes, CDs are more irrelevant than ever. In fact, in 2011 more people in the United States downloaded their music than bought physical singles and albums.

So what to do with your piles of old CDs? Trade them back to Amazon and buy new digital albums. Starting today, CDs are included in the company’s Trade-In Program, which lets you send in old, unwanted stuff for Amazon credit.

Not that you have to buy digital albums. You can spend your Amazon credit on anything that catches your eye, like an Urkel “Did I do that?” mousepad.

Previously, Amazon users were able to trade-in items such as DVDs, Kindles and textbooks, which begs the question: Why accept CDs now? SmartMoney has a theory. In general, people spend about 40% more than the value of a gift card when shopping. As there aren’t exactly a lot of vendors lining up to buy your used CDs, Amazon can set itself up as the default destination for people’s old Third Eye Blind albums.

Yes, the market for old CDs isn’t huge, but if you’re the only buyer in town and your customers are willing to spend an extra 40% on other products, you’ve got yourself a nice little business model. Who knows, maybe they’ll make a little money on the CDs themselves — someone out there has to be looking to spend 90 cents on Chris Gaines’ Greatest Hits.